Hitherto, melting kneading devolatilizing extruders for a resin raw material are disclosed in, for example, Patent Literature 1 and Patent Literature 2.
Patent Literature 1 discloses a configuration in which a kneading portion and a devolatilizing portion are alternately provided in a plurality of places, a vacuum state is brought about in the devolatilizing portion, and devolatilization is performed by transporting and kneading of a screw in the devolatilizing portion.
On the other hand, similarly to Patent Literature 1, Patent Literature 2 discloses an apparatus, which has a kneading flight twisted so that a raw material can be transferred to the downstream, in a devolatilization region where air-tightness is maintained in a filling portion by a raw material, and which kneads the material to separate a volatile component while the material is fed the downstream. The apparatus disclosed in Patent Literature 2 is shown in FIG. 11. The extruder has a rotatable screw 102 within a cylinder 101 including a vacuum vent 103 which sucks an inside of the cylinder into a negative pressure state. The raw material supplied into the extruder is transported to the kneading portion 104 by a screw inserted into the cylinder 101, is melted in the kneading portion 104 while a shearing force is added thereto, and is transported to the downstream. In the devolatilization region 105 which is brought into a negative pressure state as air is sucked through from the vacuum vent 103, a volatile component contained in the molten raw material is separated from the molten raw material and is removed from the extruder.
In Patent Literature 2, it is reported that the volatile component contained can be more efficiently removed by installing a screw segment 106 having surface renewability (allowing a molten raw material which is not exposed to ambient air to be exposed to ambient air when a raw material is kneaded), in the devolatilization region 105 where air-tightness is maintained, and by transporting the raw material to the downstream while kneading the raw material. A front view of the screw segment of Patent Literature 2 which has surface renewability is shown in FIG. 12(a), and a side view thereof is shown in FIG. 12(b). The screw segment 106 is composed of two rotor blade segments having a pair of kneading flights which protrude in mutually opposite directions in a radial direction, and the screw segment 106 has a lower tip portion 107 with large tip clearance with the inner wall of the cylinder and a high tip portion 108 with small tip clearance. By forming a thin film of a raw material on the inner wall of the cylinder in the lower tip portion 107, and by scraping off the thin film formed by the high tip portion 108, it is possible to repeatedly perform surface renewal to more effectively promote devolatilization.
Patent Literature 1: Japanese Patent No. 3857411
Patent Literature 2: JP-A-2006-1252